In communication systems such as Wideband Code Division Multiple Access (registered trademark) (WCDMA), Long-Term Evolution (LTE), and LTE-Advanced (LTE-A) by the Third Generation Partnership Project (3GPP), or a wireless LAN and Worldwide Interoperability for Microwave Access (WiMAX) by the Institute of Electrical and Electronics Engineers (IEEE), a base station (a cell, a transmission station, a transmission apparatus, or eNodeB) and a terminal (a mobile terminal, a reception station, a mobile station, a reception apparatus, or user equipment (UE)) respectively include a plurality of transmission and reception antennae, and spatially multiplex a data signal by applying a multi-input multi-output (MIMO) technique, so as to realize high-speed data communication.
In the communication systems, in order to realize data communication between the base station and the terminal, the base station is required to perform various controls on the terminal. For this reason, the base station notifies the terminal of control information by using a predetermined resource, so as to perform data communication via a downlink and an uplink. For example, the base station realizes data communication by notifying the terminal of resource assignment information, modulation and coding information of a data signal, spatial multiplexing number information of a data signal, transmission power control information, and the like. Such control information may be transmitted by using a method disclosed in NPL 1.
In addition, as a communication method in a downlink using the MIMO technique, various methods may be used, and, for example, a multiuser MIMO method of assigning the same resource to different terminals, or a coordinated multipoint or cooperative multipoint (CoMP) method in which a plurality of base stations perform data communication in cooperation with each other may be used.
FIG. 22 is a diagram illustrating an example in which the multiuser MIMO method is performed. In FIG. 22, a base station 2201 performs data communication with a terminal 2202 via a downlink 2204, and performs data communication with a terminal 2203 via a downlink 2205. In this case, the terminal 2202 and the terminal 2203 perform data communication by multiuser MIMO. The same resource is used in the downlink 2204 and the downlink 2205. The resource consists of frequency and time components. In addition, the base station 2201 controls beams of each of the downlink 2204 and the downlink 2205 by using a precoding technique or the like, and thus maintains mutual orthogonality or reduces co-channel interference. Consequently, the base station 2201 can realize data communication using the same resource with the terminal 2202 and the terminal 2203.
FIG. 23 is a diagram illustrating an example in which a downlink CoMP method is performed. FIG. 23 illustrates a case where a radio communication system using a heterogeneous network configuration consists of a macro base station 2301 having wide coverage and a remote radio head (RRH) 2302 having coverage narrower than the coverage of the macro base station 2301. Here, a case is assumed in which the coverage of the macro base station 2301 is configured to include part of or the whole coverage of the RRH 2302. In the example illustrated in FIG. 23, a heterogeneous network configuration consists of the macro base station 2301 and the RRH 2302, and data communication is performed with a plurality of terminals 2304 in cooperation with each other via a downlink 2305 and a downlink 2306. The macro base station 2301 is connected to the RRH 2302 via a line 2303 and can thus transmit and receive a control signal or a data signal to and from the RRH 2302. As the line 2303, a wired line such as an optical fiber or a wireless line using a relay technique may be used. In this case, the macro base station 2301 and the RRH 2302 use the same partial or whole frequency (resource), and thus comprehensive spectral efficiency (transmission capacity) within an area of coverage determined by the macro base station 2301 can be improved.
The terminal 2304 can perform single-cell communication with the base station 2301 or the RRH 2302 in a case of being located around the base station 2301 or the RRH 2302. In addition, in a case where the terminal 2304 is located around an end (cell edge) of coverage determined by the RRH 2302, a countermeasure of co-channel interference from the macro base station 2301 is necessary. As multi-cell communication (coordinated communication, multi-point communication, or CoMP) between the macro base station 2301 and the RRH 2302, a method has been examined in which interference with the terminal 2304 in a cell edge region is reduced or minimized by using the CoMP method in which the macro base station 2301 and the RRH 2302 cooperate with each other. For example, as such a CoMP method, a method disclosed in NPL 2 has been examined.
FIG. 24 is a diagram illustrating an example in which an uplink CoMP method is performed. FIG. 24 illustrates a case where a radio communication system using a heterogeneous network configuration consists of a macro base station 2401 having wide coverage and a remote radio head (RRH) 2402 having coverage narrower than the coverage of the macro base station 2401. Here, a case is assumed in which the coverage of the macro base station 2401 is configured to include part of or the whole coverage of the RRH 2402. In the example illustrated in FIG. 24, a heterogeneous network configuration consists of the macro base station 2401 and the RRH 2402, and data communication is performed with a plurality of terminals 2404 in cooperation with each other via an uplink 2405 and an uplink 2406. The macro base station 2401 is connected to the RRH 2402 via a line 2403 and can thus transmit and receive, a reception signal, a control signal, or a data signal to and from the RRH 2402. As the line 2403, a wired line such as an optical fiber or a wireless line using a relay technique may be used. In this case, the macro base station 2401 and the RRH 2402 use the same partial or whole frequency (resource), and thus comprehensive spectral efficiency (transmission capacity) within an area of coverage determined by the macro base station 2401 can be improved.
The terminal 2404 can perform single-cell communication with the base station 2401 or the RRH 2402 in a case of being located around the base station 2401 or the RRH 2402. Here, in a case where the terminal 2404 is located around the base station 2401, the base station 2401 receives and demodulates a signal which is received via the uplink 2405. Alternatively, in a case where the terminal 2404 is located around the RRH 2402, the RRH 2402 receives and demodulates a signal which is received via the uplink 2406. In addition, in a case where the terminal 2404 is located around an end (cell edge) of coverage determined by the RRH 2402 or is located around a middle point between the base station 2401 and the RRH 2402, the macro base station 2401 receives a signal which is received via the uplink 2405, and the RRH 2402 receives a signal which is received via the uplink 2406. Then, the macro base station 2401 and the RRH 2402 perform transmission and reception of the signals received from the terminal 2404 via the line 2403, so as to combine the signals received from the terminal 2404 with each other and to demodulate the combined signal. Through this process, performance of data communication is expected to be improved. This is a method called joint reception (JR), and performance of data communication in a cell edge region or a region around a middle point between the macro base station 2401 and the RRH 2402 can be improved by using the CoMP method in which the macro base station 2401 and the RRH 2402 cooperate with each other as uplink multi-cell communication (coordinated communication, multi-point communication, or CoMP).